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Abstract:

The method for producing a photovoltaic cell includes applying, on a
partial region of one surface side of a semiconductor substrate, a first
p-type diffusion layer forming composition including a p-type
impurity-containing glass powder and a dispersion medium; applying, on at
least a region other than the partial region on the surface of the
semiconductor substrate, a second p-type diffusion layer forming
composition which includes a p-type impurity-containing glass powder and
a dispersion medium and in which a concentration of the p-type impurity
is lower than that of the first p-type diffusion layer forming
composition, where the first p-type diffusion layer forming composition
is applied; heat-treating the semiconductor substrate on which the first
p-type diffusion layer forming composition and the second p-type
diffusion layer forming composition are applied to form a p-type
diffusion layer; and forming an electrode on the partial region.

Claims:

1. A method for producing a photovoltaic cell, comprising: applying, on a
partial region of one surface side of a semiconductor substrate, a first
p-type diffusion layer forming composition including a p-type
impurity-containing glass powder and a dispersion medium; applying, on at
least a region other than the partial region on the surface of the
semiconductor substrate where the first p-type diffusion layer forming
composition is applied, a second p-type diffusion layer forming
composition which includes a p-type impurity-containing glass powder and
a dispersion medium and in which a concentration of the p-type impurity
is lower than that of the first p-type diffusion layer forming
composition; heat-treating the semiconductor substrate on which the first
p-type diffusion layer forming composition and the second p-type
diffusion layer forming composition are applied to form a p-type
diffusion layer; and forming an electrode on the partial region.

2. The method for producing a photovoltaic cell according to claim 1,
wherein the p-type impurity includes at least one kind of element
selected from the group consisting of B (boron), Al (aluminum), and Ga
(gallium).

3. The method for producing a photovoltaic cell according to claim 1,
wherein the p-type impurity-containing glass powder includes, at least
one kind of p-type impurity-containing material selected from the group
consisting of B2O3, Al2O3, and Ga2O3, and
at least one kind of glass component material selected from the group
consisting of SiO2, K2O, Na2O, Li2O, BaO, SrO, CaO,
MgO, BeO, ZnO, PbO, CdO, V2O5, SnO, ZrO2, TiO2, and
MoO.sub.3.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. 119(e) to
Provisional U.S. Patent Applications No. 61/414,585, filed Nov. 17, 2010,
the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method for producing a
photovoltaic cell.

[0004] 2. Description of the Related Art

[0005] In the producing of a photovoltaic cell having a pn conjunction in
the related art, for example, a p-type impurity is diffused into an
n-type semiconductor substrate formed of silicon or the like and thereby
a p-type diffusion layer is formed. Accordingly, the pn conjunction is
formed.

[0006] Particularly, as a structure of photovoltaic cell for increasing
conversion efficiency, a selective emitter structure, in which the
impurity concentration in a region other than the region directly under
an electrode is made to be lower than the impurity concentration in the
region directly under the electrode, is disclosed (for example, refer to
L. Debarge, M. Schott, J.C. Muller, R. Monna, Solar Energy Materials &
Solar Cells 74 (2002) 71-75). In the structure, since the region in which
the impurity concentration is high is formed directly under the electrode
(hereinafter, the region is referred to as "selective emitter"), the
contact resistance between a metallic electrode and the silicon can be
reduced, on the other hand, in regions other than the region directly
under the metallic electrode, the impurity concentration is low, such
that it is possible to improve the conversion efficiency of the
photovoltaic cell.

[0007] To form the selective emitter structure described above, there is
necessary a complicated process in which plural diffusions and partial
etching through masking or the like are repeated (for example, refer to
Japanese Patent Application Laid-Open (JP-A) No. 2004-193350).

[0008] In addition, a method in which a diffusing agent is applied onto a
substrate with a plurality of impurity concentrations through an ink jet
method, and impurities are diffused is disclosed (for example, refer to
JP-A No. 2004-221149).

SUMMARY OF THE INVENTION

[0009] An embodiment according to the present invention is a method for
producing a photovoltaic cell, including:

[0010] applying, on a partial region of one surface side of a
semiconductor substrate, a first p-type diffusion layer forming
composition including a p-type impurity-containing glass powder and a
dispersion medium;

[0011] applying, on at least a region other than the partial region on the
surface of the semiconductor substrate where the first p-type diffusion
layer forming composition is applied, a second p-type diffusion layer
forming composition which includes a p-type impurity-containing glass
powder and a dispersion medium and in which a concentration of the p-type
impurity is lower than that of the first p-type diffusion layer forming
composition;

[0012] heat-treating the semiconductor substrate on which the first p-type
diffusion layer forming composition and the second p-type diffusion layer
forming composition are applied to form a p-type diffusion layer; and

[0013] forming an electrode on the partial region.

DETAILED DESCRIPTION OF THE INVENTION

[0014] In the method disclosed in JP-A No. 2004-193350, to form the
selective emitter structure, processes for the pattern formation and the
etching are necessary, and therefore the number of process is apt to
increase. In addition, in the ink jet method disclosed in JP-A No.
2004-221149, a dedicated device including a plurality of heads is
necessary, and the control of spraying from each head also becomes
complex.

[0015] An object of the invention is to provide a method for producing a
photovoltaic cell, which allows a photovoltaic cell having a selective
emitter structure to be produced by a simple method without requiring a
complicated device.

[0016] The above-stated problems are addressed by the following means.

<1> A method for producing a photovoltaic cell, including:
applying, on a partial region of one surface side of a semiconductor
substrate, a first p-type diffusion layer forming composition including a
p-type impurity-containing glass powder and a dispersion medium;
applying, on at least a region other than the partial region on the
surface of the semiconductor substrate where the first p-type diffusion
layer forming composition is applied, a second p-type diffusion layer
forming composition which includes a p-type impurity-containing glass
powder and a dispersion medium and in which a concentration of the p-type
impurity is lower than that of the first p-type diffusion layer forming
composition; heat-treating the semiconductor substrate on which the first
p-type diffusion layer forming composition and the second p-type
diffusion layer forming composition are applied to form a p-type
diffusion layer; and forming an electrode on the partial region.
<2> The method for producing a photovoltaic cell according to
<1>, wherein the p-type impurity includes at least one kind of
element selected from the group consisting of B (boron), Al (aluminum),
and Ga (gallium). <3> The method for producing a photovoltaic cell
according to <1> or <2>, wherein the p-type
impurity-containing glass powder includes, at least one kind of p-type
impurity-containing material selected from the group consisting of
B2O3, Al2O3, and Ga2O3, and at least one
kind of glass component material selected from the group consisting of
SiO2, K2O, Na2O, Li2O, BaO, SrO, CaO, MgO, BeO, ZnO,
PbO, CdO, V2O5, SnO, ZrO2, TiO2, and MoO3.

[0017] In the present specification, the term "process" denotes not only
independent processes but also processes that cannot be clearly
distinguished from other processes as long as a purpose is accomplished
by the process. And "from . . . to . . . " denotes a range including each
of the minimum value and the maximum value of the values described in
this expression. Unless specifically indicated, when an each ingredient
of a composition includes plural materials, a content of the each
ingredient of the composition denotes total amount of the plural
materials including the composition.

[0018] The configuration of a method for producing a photovoltaic cell of
the invention includes a process of applying a first p-type diffusion
layer forming composition including a p-type impurity-containing glass
powder and a dispersion medium onto a partial region on one surface side
of a semiconductor substrate, a process of applying a second p-type
diffusion layer forming composition which includes a p-type
impurity-containing glass powder and a dispersion medium and in which the
concentration of the p-type impurity is lower than that of the first
p-type diffusion layer forming composition, onto at least a region other
than the partial region on the surface of the semiconductor substrate
where the first p-type diffusion layer forming composition, a process of
heat-treating the semiconductor substrate onto which the first p-type
diffusion layer forming composition and the second p-type diffusion layer
forming composition are applied to form a p-type diffusion layer, forming
an electrode on the partial region, and optionally other processes as
necessary.

[0019] First, a first p-type diffusion layer forming composition, and a
second p-type diffusion layer forming composition (hereinafter, these are
simply referred to as "p-type diffusion layer forming composition") of
the invention will be described, and then, a method for forming a
selective emitter structure using the p-type diffusion layer forming
composition will be described.

[0020] The p-type diffusion layer forming composition includes at least
one kind of p-type impurity-containing glass powder, and at least one
kind of dispersion medium, and may optionally include other additives in
consideration of the coating properties.

[0021] Here, the p-type diffusion layer forming composition represents a
material that includes a p-type impurity and that is able to form a
p-type diffusion layer through being applied onto a silicon substrate and
then thermally diffusing the p-type impurity. When the p-type diffusion
layer forming composition is used, the p-type diffusion layer is formed
at a desired portion.

[0022] Since a p-type impurity component in the glass powder is hardly
volatilized even during sintering, a p-type diffusion layer is prevented
from also being formed on the rear surface or side face, rather than on
the front surface alone due to the generation of volatile gases. It is
assumed that the reason for this is that the p-type impurity component
combines with an element in a glass powder, or is absorbed into the
glass, as a result of which the p-type impurity component is hardly
volatilized.

Glass Powder

[0023] The term "p-type impurity" included in the glass powder refers to
an element which is capable of forming a p-type diffusion layer by doping
thereof on a silicon substrate. As the p-type impurity, elements of Group
XIII of the periodic table can be used. Examples of the p-type impurity
include B (boron), Al (aluminum), and Ga (gallium).

[0024] Examples of the p-type impurity-containing material include
B2O3, Al2O3, and Ga2O3. At least one
selected from B2O3, Al2O3, and Ga2O3 is
preferably used.

[0025] Further, the melting temperature, softening point, glass-transition
point, chemical durability or the like of the glass powder can be
controlled by adjusting the component ratio, if necessary. Further, the
glass powder preferably contains the components mentioned below.

[0027] Specific examples of the p-type impurity-containing glass powder
include those including both the p-type impurity-containing material and
the glass component material such as, for example, B2O3 based
glass which includes B2O3 as the p-type impurity such as
B2O3--SiO2 (the p-type impurity-containing material and
the glass component material are listed in this order, and are listed in
the same order below) based glass, B2O3--ZnO based glass,
B2O3--PbO based glass, single B2O3 based glass;
Al2O3 based glass which includes Al2O3 as the
acceptor element such as Al2O3--SiO2 based glass; and
Ga2O3 based glass which includes Ga2O3 as the
acceptor element such as Ga2O3--SiO2 based glass.

[0028] The p-type impurity-containing glass powder may include two or more
p-type impurity-containing materials such as
Al2O3--B2O3, Ga2O3--B2O3 or the
like.

[0029] Although composite glasses containing one or two components have
been exemplified in the above, glass powder containing three or more
components, such as B2O3--SiO2--Na2O, may also be
used as necessary.

[0030] The content of the glass component material in the glass powder is
preferably appropriately set taking into consideration the melting
temperature, the softening point, the glass-transition point, and
chemical durability. Generally, the content of the glass component
material is preferably from 0.1% by mass to 95% by mass, and more
preferably from 0.5% by mass to 90% by mass.

[0031] The softening point of the glass powder is preferably in the range
of from 200° C. to 1000° C., and more preferably from
300° C. to 900° C., from the viewpoint of diffusivity
during the diffusion treatment, and dripping.

[0032] The shape of the glass powder includes a substantially spherical
shape, a flat shape, a block shape, a plate shape, a scale-like shape,
and the like. From the viewpoint of coating property and uniform
dispersion property, it is preferably a spherical shape, a flat shape, or
a plate shape.

[0033] The average particle diameter of the glass powder is preferably 100
μm or less. When a glass powder having an average particle diameter of
100 μm or less is used, a smooth coated film can be easily obtained.
Further, the average particle diameter of the glass powder is more
preferably 50 μm or less and further preferably 10 μm or less. The
lower limit of the average particle diameter is not particularly limited,
and preferably 0.01 μm or more.

[0034] The average particle diameter of the glass powder means the mean
volume diameter, and may be measured by laser diffraction particle size
analyzer.

[0035] The p-type impurity-containing glass powder is prepared according
to the following procedure.

[0036] First, raw materials are weighed and placed in a crucible. Examples
of the material for the crucible include platinum, platinum-rhodium,
iridium, alumina, quartz and carbon, which are appropriately selected
taking into consideration the melting temperature, atmosphere, reactivity
with melted materials, and the like.

[0037] Next, the raw materials are heated to a temperature corresponding
to the glass composition in an electric furnace, thereby preparing a
solution. At this time, stirring is preferably applied such that the
solution becomes homogenous.

[0038] Subsequently, the obtained solution is allowed to flow on a
zirconia or carbon plate or the like to result in vitrification of the
solution.

[0039] Finally, the glass is pulverized into a powder. The pulverization
can be carried out by using a known method such as using a jet mill, a
bead mill, or a ball mill.

[0040] The content of the p-type impurity-containing glass powder in the
p-type diffusion layer forming composition is determined taking into
consideration coatability, diffusivity of p-type impurities, and the
like. Generally, the content of the glass powder in the p-type diffusion
layer forming composition is preferably from 0.1% by mass to 95% by mass,
more preferably from 1% by mass to 90% by mass, still more preferably
from 1.5% by mass to 85% by mass, and furthermore preferably from 2% by
mass to 80% by mass.

Dispersion Medium

[0041] Hereinafter, a dispersion medium will be described.

[0042] The dispersion medium is a medium which disperses the glass powder
in the composition. Specifically, a binder, a solvent or the like is
employed as the dispersion medium.

[0046] The content of the dispersion medium in the p-type diffusion layer
forming composition is determined taking into consideration coatability
and p-type impurity concentration.

[0047] The viscosity of the p-type diffusion layer forming composition is
preferably from 10 mPas to 1,000,000 mPas, and more preferably from 50
mPas to 500,000 mPas, from the viewpoint of coatability.

[0048] In the present invention, at least two kinds of p-type diffusion
layer forming compositions in which the concentration of the p-type
impurity is different are used. In the present invention, for example, a
first p-type diffusion layer forming composition having a high
concentration of p-type impurity applied onto an electrode forming region
on one surface side of a semiconductor substrate, and a second p-type
diffusion layer forming composition having a low concentration of p-type
impurity applied onto a region other than the electrode forming region of
the same surface or the entire surface thereof. Then, the p-type impurity
in the p-type diffusion layer forming composition is made to diffuse into
the semiconductor substrate through a heating treatment and thereby the
p-type diffusion layer is formed. Accordingly, it is possible to
efficiently form a selective emitter having a high concentration of
p-type impurity in the electrode forming region.

[0049] In regard to the concentration of the p-type impurity in the first
p-type diffusion layer forming composition and the second p-type
diffusion layer forming composition, as long as the p-type impurity
concentration remains greater in the first p-type diffusion layer forming
composition, the p-type impurity concentration of the first p-type
diffusion layer forming composition is not particularly limited. From the
viewpoint of formation efficiency of a high concentration p-type
diffusion layer and the photovoltaic efficiency thereof, it is preferable
that a ratio of the concentration of the p-type impurity in the first
p-type diffusion layer forming composition to the concentration of p-type
impurity in the second p-type diffusion layer forming composition (first
p-type diffusion layer forming composition/second p-type diffusion layer
forming composition) is from 1.1 to 50, and more preferably from 1.2 to
20.

[0050] In addition, the concentration of the p-type impurity in the p-type
diffusion layer forming composition may be adjusted by selecting the
appropriate content rate of glass powder, the content rate of the p-type
impurity contained in the glass powder, or the like.

Method for Producing Photovoltaic Cell

[0051] First, a damage layer on the surface of the silicon substrate is
removed through etching using an acidic or alkalic solution.

[0052] Next, a protective film formed of a silicon oxide film or a silicon
nitride film on one surface side of the silicon substrate is formed.
Here, the silicon oxide film may be formed, for example, by a normal
pressure CVD method using silane gas and oxygen. In addition, the silicon
nitride film may be formed, for example, by a plasma CVD method using
silane gas, ammonia gas, and nitrogen gas.

[0053] Next, a minute concavo-convex structure called a texture structure
is formed on the surface of the side where the protective film of the
silicon substrate is not formed. The texture structure may be formed, for
example, by immersing the silicon substrate on which the protective film
is formed in liquid including potassium hydroxide and isopropyl alcohol
(IPA) at approximately 80° C.

[0054] Subsequently, the silicon substrate is immersed in a hydrofluoric
acid and thereby the protective film is etched and removed.

[0055] Next, a p-type diffusion layer is formed on an n-type silicon
substrate and thereby a pn conjunction is formed. In the present
invention, the p-type diffusion layer forming composition is applied onto
an electrode forming region (region in which an electrode is expected to
be formed) in which a light receiving surface electrode is formed, and
thereby the impurity concentration in the electrode forming region is
made to be higher than a region other than the electrode forming region.

[0056] In the present invention, the shape and size of the electrode
forming region having a high impurity concentration may be selected
appropriately according to the structure of the photovoltaic cell that is
composed. The shape, for example, may be a line shape or the like.

[0057] In the present invention, the p-type diffusion layer forming
composition layer is formed on the n-type silicon substrate by a process
of applying the first p-type diffusion layer forming composition in the
electrode forming region of the n-type silicon substrate in which the
light receiving surface electrode is formed, and a process of applying
the second p-type diffusion layer forming composition in at least a
region other than the electrode forming region.

[0058] Onto the electrode forming region, the first p-type diffusion layer
forming composition may be applied alone, or both of the first p-type
diffusion layer forming composition and the second p-type diffusion layer
forming composition may be applied.

[0059] In addition, the sequence of applying the first p-type diffusion
layer forming composition and the second p-type diffusion layer forming
composition is not particularly limited. That is, after applying the
first p-type diffusion layer forming composition in the electrode forming
region, the second p-type diffusion layer forming composition may be
applied onto the entirety of the light receiving surface or a region
other than the electrode forming region. In addition, after applying the
second p-type diffusion layer forming composition to the entirety of the
light receiving surface or the region other than the electrode forming
region, the first p-type diffusion layer forming composition may be
applied onto the electrode forming region.

[0060] A method of applying the first p-type diffusion layer forming
composition and second p-type diffusion layer forming composition is not
particularly limited, and a generally used method may be used. For
example, a printing method such as a screen printing method or a gravure
printing method, a spinning method, a brush coating, a spraying method, a
doctor blade method, a roll coater method, an ink jet method, or the like
may be used. Furthermore, the method for applying the first p-type
diffusion layer forming composition and the second p-type diffusion layer
forming composition may be the same as each other or be different from
each other.

[0061] The amount applied of the first and second p-type diffusion layer
forming compositions is not particularly limited. For example, the amount
of the glass powder may be set to from 0.01 g/m2 to 100 g/m2,
and more preferably to from 0.1 g/m2 to 10 g/m2. In addition, a
ratio of the application amount of the second p-type diffusion layer
forming composition to the application amount of the first p-type
diffusion layer forming composition (second p-type diffusion layer
forming composition/first p-type diffusion layer forming composition) is
not particularly limited, and may be appropriately selected in order for
the p-type diffusion layer to be formed to have a desired impurity
concentration.

[0062] After applying the p-type diffusion layer forming composition on
the silicon substrate, a heating process which removes at least a part of
the dispersion medium may be provided. In the heating process, for
example, when a heating treatment is performed at from 100° C. to
200° C., it is possible to volatilize at least a part of a
solvent. In addition, for example, at least a part of a binder may be
removed through a heating treatment at from 200° C. to 500°
C.

[0063] Next, the p-type diffusion layer is formed through a heat treatment
of the silicon substrate on which the p-type diffusion layer forming
composition is applied. Through the heat treatment, the p-type impurity
is diffused from the p-type diffusion layer forming composition onto the
silicon substrate, and thereby the high concentration p-type diffusion
layer is formed in the electrode forming region in which the light
receiving surface electrode is formed, and a low concentrated p-type
diffusion layer is formed in a region other than the electrode forming
region.

[0064] Here, it is preferable that the temperature of the heat treatment
is from 800° C. to 1100° C., more preferably from
850° C. to 1100° C., and further more preferably from
900° C. to 1100° C.

[0065] A glass layer remains on the silicon substrate on which the p-type
diffusion layer is formed as described abve, but it is preferable to
remove the glass layer. For the removal of the glass layer, a known
method such as a method of immersing the silicon substrate in an acid
such as a hydrofluroic acid, or a method of immersing the silicon
substrate in an alkali such as sodium hydroxide may be exemplified.

[0066] Next, on the light receiving surface on which p-type diffusion
layer is formed, an antireflective film is formed. Here, as the
antireflective film, for example, a nitride film formed by the plasma CVD
method may be used.

[0067] Next, electrodes are formed on the rear surface of the substrate
and on the light receiving surface. The generally used method may be used
to form the electrodes without being particularly limited.

[0068] For example, in regard to a light receiving surface electrode (a
surface electrode), the surface electrode may be formed on the electrode
forming region in which the high concentration p-type diffusion layer is
formed, by applying a metallic paste for the surface electrode, which
includes metallic particles and glass particles, onto the electrode
forming region to have a desired shape and by sintering the applied
metallic paste.

[0069] As the metallic paste for the surface electrode, for example, a
silver paste or the like that is generally used in the present technical
field may be used.

[0070] In addition, a rear surface electrode may be formed by applying,
for example, a paste for the rear surface electrode, which includes a
metal such as aluminum, silver, and copper, and drying the paste, and by
baking the dried paste. At this time, a silver paste for the formation of
the silver electrode may be provided on a part of the rear surface for
connection between cells in a module process.

EXAMPLES

[0071] Hereinafter, the present invention will be described in detail with
reference to examples, but the present invention is not limited to the
examples. In addition, if not particularly mentioned, as chemicals, a
reagent is used as a whole. In addition, "part" and "%" are based on a
mass.

Example 1

[0072] A glass powder whose particle shape is substantially spherical,
average particle diameter is 1.5 μm and softening point is about
810° C. (including B2O3, SiO2, CaO, MgO, and BaO as
main components, with a content rate of 30%, 40%, 10%, 10%, and 10%,
respectively), ethyl cellulose, and terpineol are blended and made into a
paste in an amount of 20 g, 8 g, and 72 g, respectively, and thereby the
first p-type diffusion layer forming composition (composition A) was
prepared. In addition, a glass powder whose particle shape is
substantially spherical, average particle diameter is 1.5 μm and
softening point is about 810° C. (including B2O3,
SiO2, CaO, MgO, and BaO as main components, with a content rate of
30%, 40%, 10%, 10%, and 10%, respectively), ethyl cellulose, and
terpineol are blended and made into a paste in the amounts of 5 g, 6 g,
and 89 g, respectively, and thereby the second p-type diffusion layer
forming composition (composition B) was prepared.

[0073] The particle shape of the glass powder was judged by observation
with a scanning electron microscope (trade name: TM-1000, manufactured by
Hitachi High-Technologies Corporation). The average diameter of the glass
powder was calculated with a laser diffraction particle size analyzer
(measurement wave length: 632 nm, trade name: LS 13 320, manufactured by
Beckman Coulter, Inc.). The softening point of the glass powder was
measured by a differential thermal analysis (DTA) curve with a Thermo
Gravimetry Differential Thermal Analyzer (trade name: DTG-60H,
manufactured by SHIMADZU CORPORATION).

[0074] Next, the composition A was applied in a line shape onto a part of
a surface of the p-type silicon substrate through screen printing, and
the applied composition A was dried at 150° C. for 10 minutes.
Subsequently, the composition B was applied onto the entirety of the same
surface of the silicon substrate through screen printing, and the applied
composition B was dried at 150° C. for 10 minutes. Then, a binder
removal treatment was performed at 350° C. for 3 minutes.

[0075] Next, a heat treatment was performed in an atmosphere at
950° C. for 10 minutes, and thereby the p-type impurity was made
to diffuse into the silicon substrate. Accordingly, the p-type diffusion
layer was formed.

[0076] Subsequently, the glass layer remaining on the surface of the
silicon substrate was removed by a hydrofluoric acid.

[0077] The average value of the sheet resistance in a portion (electrode
forming region) where the composition A was applied was 58
Ω/square, and the average value of the sheet resistance in the
other portion was 127 Ω/square. From these results, it can be seen
that the resistance in a portion where the composition A was applied is
selectively reduced. The sheet resistance was measured by a four probe
method with a low resistance meter (trade name: Loresta-EP MCP-T360,
manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[Manufacturing Photovoltaic Cell]

[0078] Using the silicon substrate in which the p-type diffusion layer was
formed, which was obtained as described, through a normal method, an
antireflective film was formed on a front surface of the silicon
substrate, a surface electrode was formed in the electrode forming
region, and a rear surface electrode was formed on a rear surface,
respectively. Accordingly, a photovoltaic cell was produced. The obtained
photovoltaic cell showed excellent photoconversion characteristics
compared to a photovoltaic cell that was not provided with an electrode
forming region (selective emitter) in which a high concentration p-type
diffusion layer was formed.

[0079] The foregoing description of the embodiments of the present
invention has been provided for the purposes of description. It is not
intended to be exhaustive or to limit the present invention to the
precise forms disclosed. Obviously, many modifications and variations
will be apparent to practitioners skilled in the art. The embodiments
were chosen and described in order to best explain the principles of the
present invention and its practical applications, thereby enabling others
skilled in the art to understand the present invention for various
embodiments and with the various modifications as are suited to the
particular use contemplated. It is intended that the scope of the present
invention be defined by the following claims and their equivalents.

[0080] All publications, patent applications, and technical standards
mentioned in this specification are herein incorporated by reference to
the same extent as if each individual publication, patent application, or
technical standard was specifically and individually indicated to be
incorporated by reference.